Wound dressing

ABSTRACT

Wound dressings suitable for negative pressure wound therapy are disclosed. The wound dressings may include a body of porous material, the body of porous material may include a plurality of cuts which provide regions of flexibility within the body. Also disclosed are methods of manufacturing and methods of using such wound dressings. In addition, such wound dressings can include a retaining mechanism removably coupled to the material and configured to retain the material in the expanded conformation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 12/443,169, filed Nov. 17, 2009, entitled LATTICE DRESSING,which is a National Phase Application of PCT Patent Application No.PCT/US2007/079529 filed Sep. 26, 2007, entitled LATTICE DRESSING, whichclaims priority to U.S. Provisional Application No. 60/826,922, filedSep. 26, 2006, entitled LATTICE DRESSING. This application is also acontinuation-in-part of U.S. patent application Ser. No. 13/202,974,filed Oct. 5, 2011, entitled DRAPEABLE WOUND DRESSING, which is aNational Phase Application of PCT Patent Application PCT/GB2010/000293,filed Feb. 19, 2010, entitled DRAPEABLE WOUND DRESSING, which claimspriority to Great Britain Application No. 0903032.1, filed Feb. 24,2009, entitled DRAPEABLE WOUND DRESSING. The contents of theaforementioned applications are hereby incorporated by reference intheir entireties as if fully set forth herein. The benefit of priorityto the foregoing applications is claimed under the appropriate legalbasis, including, without limitation, under 35 U.S.C. § 119(e).

BACKGROUND OF THE INVENTION Field of the Invention

This application describes embodiments of apparatuses, methods,materials, methods of manufacture, and systems for the treatment ofwounds, specifically to aid in packing and treating wounds.

This application further relates to improved wound dressing materials.In particular this application relates to wound dressing materials withimproved drapeability, which allows them to more easily conform to theshape of a surface over which they are placed. Especially, but notexclusively, the present application relates to foam materials,especially those suitable for use in negative pressure wound therapy(NPWT).

Description of the Related Art

Wound dressings are commonly manufactured from sheet materials. Thesematerials include transparent films and adhesives and opaque foams andfibres. These materials generally retain their transparency or opacityupon fluid absorption, the exception being carboxymethylcellulose-basedhydrofibre (which is initially opaque and becomes transparent when wet).Wound dressings which rely upon a foam element for exudate managementare opaque and require removal and exchange for a new dressing duringevery wound inspection. This is a disadvantage of opaque dressings, forexample, including a foam element. Foam-based dressings also havelimited extensibility due to the mechanical properties inherent in amaterial of foam structure; this can cause problems when attempting todress locations of high curvature. In spite of these performancedisadvantages, the use of foam-based wound dressings or dressingelements dominates woundcare. This may be due to their excellentabsorbency, low dry weight, cut-ability and mouldability. Limitedextensibility is not restricted to foams; this is also a property of thefilms commonly applied in medical devices.

The single-axis lattice cutting of monolithic materials, including thesheet materials utilised in wound dressings has been disclosed in(GB821,959). However, once cut, these materials are not extended in anymanner until post-application to the wound, and only then as a result ofthe flexing of the limb or other part of the body on which the dressingis worn. Whilst this type of dressing does enable some ease of movementfor the patient, the material only permits minimal visibility of thewound. Additionally, the size of apertures and thus the permeability ofthe material, particularly important for the release of exudates fromthe wound, cannot be controlled.

There is a need for a wound dressing which can be established in anextended conformation both prior to application and during applicationto a wound.

There is a need for a wound dressing which can be retained within adefined extended conformation both prior to application and duringapplication to a wound.

There is a need for a wound dressing which allows visualisation of thewound immediately upon application of the dressing.

There is a need for a wound dressing which has a controlled apertureprofile, which enables control of exudate egress.

There is a need for a wound dressing which has a controlled contractileprofile for promoting wound closure.

NPWT is a relatively new treatment for open wounds. Typically in NPWTthe wound cavity or surface is filled or covered with a material thatallows the transmission of a partial vacuum (i.e. does not completelycollapse) to the wound bed when a negative pressure is applied to thewound area, and also allows fluids to pass from the wound bed towardsthe source of negative pressure. There are two primary approaches toNPWT, gauze or foam types. The gauze type (also referred to as theChariker-Jeter technique) involves the use of a drain wrapped in gauzetopped by a sealed dressing. The foam type involves the use of foamplaced over or in the wound. The present invention is directedprimarily, but not exclusively, towards the foam type of NPWT.

In foam based NPWT the wound is filled or covered with a porous,compressible foam packing material and covered over and sealed withflexible sheet (a drape) that is fairly impermeable to fluids. A tube isinserted under or through the drape into the wound site and its distalend is connected to a vacuum source (commonly a pump). The wound cavity,enclosed by the drape and tissue, contracts under the force ofatmospheric pressure and compresses the packing material visibly. Grosstissue movement ceases after a few tens of seconds and fluid flow fromthe wound (withdrawn from the tissue) ensues. The fluid is transmittedthrough the packing material and up the vacuum tube to a collectionreceptacle positioned between the distal end of the tube and the vacuumsource. The material mechanically supports the tissue to which it isapplied, and also allows the free flow of fluids away from the site whena vacuum is applied, even when compressed. A good material for thisapplication is hydrophobic, reticulated polyurethane foam of very highfree internal volume. However, articles of high free internal volumetend to be poorly drapeable due to the requirement for their structureto mechanically support their high free internal volume, and this is thecase in current foams applied in NPWT.

The foams, which in other regards are near optimal for NPWT, are verypoorly conformable to the site of application especially prior to theapplication of a covering drape and vacuum being applied. This is truefor cavity wounds of concave geometry, and surface wounds, e.g. to theextremities, of convex geometry.

Monolithic articles of high free internal volume are able to supporttheir own external dimensions by virtue of their mechanical properties,i.e. they are relatively stiff. This factor has the side effect ofmaking such solid objects poorly drapeable and this is not desirable forall applications. For some applications, the mechanical integrity of thestructure is not required at the scale of the monolith itself.

For medical applications involving the application of articles to thebody, both good drapeability and good resistance to compression underloading are desirable attributes.

SUMMARY OF THE INVENTION

The visibility through an opaque material can be increased by thecreation of apertures through it. However, the creation of apertures,for example by hole-punching, has the disadvantages of resulting in thegeneration of waste and also the mechanical weakening of the material.By forming through slits in a material, these slits being capable ofexpanding to form apertures on extension of the material, we have beenable to achieve both increased visibility of the wound and increasedextensibility of the material, without significant material waste. Inthis manner, it is also possible to achieve extension of the slit toform a circular hole without mechanically weakening the material.

Therefore, according to an aspect of the invention there is provided alattice comprising a material having at least one slit, the slit beingcapable of expansion into an aperture, the lattice having

-   -   i) a first conformation, wherein the slit is substantially        closed, and    -   ii) a second conformation, wherein the lattice is stretched by        the application of an extensive force expanding the slit to form        an aperture having a first dimension.

Material having a slit or plurality of slits is referred to as alattice, and prior to extension of the material, the lattice is referredto as being in a “first conformation” or “initial conformation” or“closed lattice conformation” wherein the slits are substantiallyclosed. A substantially closed slit is a slit which has a conformationthat allows no or substantially no visual inspection of the woundthrough the lattice with the naked eye.

Preferably, the material is a polyurethane foam or a silicone elastomer,for example.

The cutting of a largely two-dimensional or flat material and athree-dimensional material to form slits can be achieved by any meansknown in the art, for example laser cutting or blade pressing. Thecutting method can be a batch process or continuous process. The cuttingarrangements of two-dimensional material are preferably two-dimensionaland along the x and y plane. The cutting arrangements ofthree-dimensional material are preferably three-dimensional and alongthe x, y and z planes.

The material may be cut so that the slits form a parallel, staggered,patterned or random arrangement.

Cuts are not restricted to any particular geometry; they may bestraight-edged or curved. Straight-edged cuts include uni-directionalarrangements, where all cuts are parallel, and multi-directionalarrangements, where all cuts are non-parallel. Curved-cuts includearrangements radiating in an outwardly direction from a central point ofthe material and describing a circumference of a circle.

Generally speaking, the greater the number of cuts and thus excise ofmaterial, the more flexible and extensible will be the lattice formedfrom the material. However, the geometry of the cutting arrangement willalso alter the mechanical properties of the material. Each differentcutting geometry will provide a lattice having somewhat differentmechanical properties and thus provide lattices of different flexibilityand extensibility.

When cutting slits into the material to form the lattice, it ispreferable that a minimum amount of material is removed. This avoids thedetrimental effect on the structural integrity, and more particularlythe mechanical strength of the lattice formed, which would otherwisehappen where a larger amount of material was removed as in the case ofthe prior art where material is removed to form holes.

Preferably, the amount of material removed to form the lattice istherefore, for example, less than about 50% of the initial materialvolume, more preferably less than about 10% of the initial materialvolume, and ideally, less than about 1% of the initial material volume.Preferably, the excise of material to form the lattice gives rise to noor substantially no visual removal of material.

When the slits have been formed by cutting the material, the surfacearea of the resulting lattice can be extended, to about 25%-75% greaterthan the surface area of the original material. Extension of the latticeopens the slits forming a plurality of apertures/structural voids of afirst dimension. The lattice in this extended form is referred to as anopen lattice or having an “open lattice conformation”, “secondconformation” or “extended conformation”.

The open lattice is established by an extensive force prior to orimmediately prior to and during attachment to the site of application,for example, a wound site.

The lattice has a top or non-wound contacting surface and a bottom orwound contacting surface. The open lattice can be made from any suitableextendible material, for example, polyurethane foam.

The extensive force can be applied to the lattice in a unidirectional,bidirectional or isotropical manner and can be achieved by any meansknown to the skilled artisan, for example by drawing between rollersrunning at differential speeds. A process of extending the material in acontrolled manner is considered particularly advantageous as this allowsapertures/structural voids of predetermined dimensions and of particularinterest to be formed.

Preferably, the lattice is extended to 25-75% of its maximum geometricalextension limit. The maximum geometrical extension limit is defined asthe point at which the rate of change of the open volume or area of theapertures is zero or substantially zero. More preferably, the lattice isextended to maximise the open volume or area of the apertures, which maynot necessarily be related to the maximum geometric extension.

Preferably, once the lattice has been extended into its secondconformation, it can be retained in this conformation by the use of aretaining means. The retaining means may be adhered to a surface of theopen lattice in any conventional manner. The retaining means can be aphysical entity, such as a structural element, for example.

In an embodiment of the invention, the structural element can be amechanically stiff backing layer, for example, the backing layer beingstiff enough to maintain the extended open lattice conformation prior toand during application of the lattice to the wound site. The backinglayer may comprise any suitable material, but is preferably plastic orpaper.

Additionally, the backing layer is easily releasable from the material.The release of the backing layer may be facilitated by a release tab orgripping portion associated with the backing layer.

The backing layer can be applied directly or indirectly to the openlattice, thus retaining and supporting it in the extended, or second oropen lattice conformation prior to and during application. The backinglayer has a sufficient mechanical stiffness to resist the inherentcontractile force of the open lattice when the extensive force isremoved, thereby retaining the lattice in the extended or open latticeconformation. Once the open lattice has been applied to the wound sitethe backing layer is removed. On removal of the backing layer, thecontractile force is transferred to the wound site promoting closure ofthe wound. Removal of the backing layer also causes the surface area ofthe lattice and the volume of the voids established therein by theextensive force to shrink.

The extensive force applied to the lattice to form the open lattice istranslated into a contractile force when the extensive force is removed.In embodiments of the invention more than about 10% of the extensiveforce is translated to a contractile force upon removal of the retainingmeans. In preferred embodiments of the invention more than about 50% ofthe extensive force is translated to a contractile force upon removal ofthe retaining means.

In this manner, a contractile force can be applied to the site ofapplication. The use of such a lattice at a wound site, either directlyor indirectly (for example, as part of a wound dressing) has theadvantage of promoting wound closure, as a result of the contractileforces pulling the edges of the wound together.

By controlling the lattice and open lattice geometry (both the cut andthe orientation of extension), it is possibly to control the geometry ofthe contractile force.

Upon removal of the retaining means, the open lattice preferablyrecovers more than 1% of the difference between its dimensions prior toextension and those same dimensions post-extension. More preferably, theopen lattice recovers more than about 5% of the difference, and ideallyrecovers more than 10% of the difference.

In this embodiment of the invention, the greater the extension of thelattice the greater will be the contractile force on removal of thebacking layer.

The invention is also concerned with the application of the open latticeboth internally and externally of the body and on normal or injuredtissue such that, following application of the open lattice, theextensive force can be released and transmitted to the attached tissueas a compressive force.

For the contraction of linear wounds, for example post-operativesurgical incisions, lattices extensible along a single axis arepreferred, as these lattices will impart contraction along a singleaxis, which when the lattice is appropriately position on the wound willbe directed perpendicular to the line of the incision. For thecontraction of two-dimensional wounds, for example chronic wounds suchas pressure ulcers, lattices extensible along multiple axes arepreferred.

Preferably, the lattice is extensible in a mechanically isotropicmanner, enabling wound contraction to be directed towards the centre ofthe wound.

Alternative embodiments provide for the backing layer to be fixed to thenon-wound contact surface of the open lattice. In this case the backinglayer is a transparent material so that visual inspection of the woundis possible through the apertures of the lattice. It will be appreciatedthat in this embodiment, no contractile force is applied to the woundfrom the open lattice.

In another embodiment of the invention, the lattice can be of a materialwhich allows it to also function as the retaining means. For example,the lattice can be made from so-called SMART materials (also referred toas shape-memory materials). The shape of SMART materials can be alteredin a controlled fashion by external stimuli, such as stress,temperature, moisture, pH, electric or magnetic fields. In embodimentsof the invention, the material is a SMART material. The lattice formedfrom the SMART material is extended into and retained in the second oropen lattice conformation by the application of one or more externalstimuli. Post-application of the open lattice to a wound site, furthercontrolled exposure of the open lattice to an external stimulus wouldresult in the open lattice fully or partially contracting to itsoriginal, “remembered” dimensions or first conformation. In a woundsite, the open lattice could also be initiated or encouraged to contractby exposure to the moisture content of a wound exudate.

In another embodiment of the invention, the structural element can be atransparent film, for example a polyurethane film, fixedly or removablyapplied to the non-wound contact surface of the open lattice or to thenon-wound contact surface and wound contact surface of the open lattice.The film is not as structurally rigid or stiff as the backing layer sothat it can not hold the open lattice in a sufficiently extended form toprovide a contractile force to promote closure of the wound if removed.Instead, the film keeps a more relaxed open conformation so that theslits remain apertures to allow visual inspection of the wound. The filmof this embodiment also acts as a bacterial barrier which isparticularly important when the lattice is administered to externalwounds.

In further embodiments, both the film and backing layer may be used. Thebacking layer forms the external non-wound contacting surface and may beremovable or fixed.

In yet a further embodiment, the lattice can be extended by hand.Gripping portions or tabs maybe provide at a periphery of the materialto give the hand purchase, for example, aiding extension of the latticeby hand. The gripping tabs can be located to allow a more effectiveextension of the lattice and formation of apertures or structural voidsfrom the slits. Once the lattice has been applied to the wound site thegripping portions are released. On release of the gripping portions, thecontractile force of the open lattice is transferred to the wound sitepromoting closure of the wound. Release of the gripping portions alsocauses the surface area of the open lattice and the volume of the voidsestablished therein, by the extensive force, to shrink. After thelattice has been secured to the wound site, the gripping portions can beremoved from the lattice by cutting, for example. This will prevent thefree ends of the gripping portions from snagging. Preferably, thelattice also has a polyeurethane film attached to both the wound andnon-wound contact surfaces of the lattice. The polyurethane film willextend with the lattice to form an open lattice and will also act as abacterial barrier.

In embodiments of the invention the lattice is a wound dressing. Inalternative embodiments of the invention the lattice can form a part(for example a layer) of a wound dressing.

In an example of the lattice being incorporated into a wound dressing, amoisture permeable top-film can be applied to the non-wound contactingsurface of the lattice (for example, by heat lamination), and theremovable backing layer applied to the top-film. The top film can be apolyurethane film, for example. Optionally, a perforated layer ofpolyurethane film can be applied to the wound contact surface of thepolyurethane foam lattice. The polyurethane film applied in this waywill prevent the polyurethane foam sticking to the wound which mayotherwise occur.

Therefore, according to a further aspect of the invention there isprovided a wound dressing consisting of or comprising the lattice of theinvention.

In an embodiment of this aspect of the invention the lattice material isa polyurethane foam and the retaining means is a backing sheet adheredtemporarily to a non wound contacting surface of the lattice (forexample, by a suitable adhesive or surface energy). The backing sheet isof a plastic material (for example, a polymeric film) or paper material(for example, reinforced paper or cardboard). The backing sheet isremoved from the open lattice once the wound dressing has been appliedto the wound by any suitable means known in the art, for example, byadhesive, sutures, staples or topical pressure.

Preferably, the material is sufficiently elastic to allow a return,unaided or unhindered, of the open lattice to the first conformation,wherein the slits are substantially closed, after being stretched,deformed, compressed, or expanded. Materials conventionally utilised inwound dressings, such as foams (for example, polyurethane foam),silicone-based material (for example, a silicone elastomer), hydrofibre,films, non-woven and woven materials, demonstrate such elasticproperties and are suitable materials.

Such elasticity results in the material exerting a spring-likecontractile force following the removal of the extensive force, forexample, by the removal of the retaining means. This contractile forceresults in the open lattice forming a “third conformation” or“contracted conformation”, in which the apertures/structural voids arecontracted to a smaller, second dimension.

In embodiments of the invention the material is a monolith.

According to a further aspect of the invention there is provided a wounddressing comprising a material having;

-   -   i) an initial conformation,    -   ii) an expanded conformation resulting from the application of        an extensive force to the material, wherein the removal of the        extensive force causes a contraction of the material, and    -   iii) the wound dressing including means for retaining the        material in the expanded conformation.

The material of this aspect of the invention is sufficiently expandableand contractible (partially or fully) from and to an initialconformation, without the requirement for the provision of slits. Forexample, the material can have elastic properties which closelyresemble, for example, LYCRA® (Invista, US).

In an embodiment of this aspect of the invention, the material isprovided with at least one slit and preferably with a plurality ofslits.

According to a further aspect of the invention there is provided amethod of promoting the closure of a wound, the method comprising thesteps of;

-   -   a) providing a material having a at least one slit to form a        lattice, the slit being capable of expansion into an aperture,        the lattice having:    -   i) a first conformation, wherein the slit is substantially        closed, and,    -   ii) a second conformation, wherein the slit is expanded into an        aperture having a first dimension,    -   iii) retaining the lattice in the second conformation prior to        application to a wound site,    -   iv) applying the lattice in its second conformation to the wound        site, and, optionally,    -   c) allowing the lattice to retract from the second conformation        towards the first conformation after application to the wound        site.

In embodiments of the invention the open lattice can be applied directlyto a wound. In alternative embodiments of the invention the open latticecan form a part (for example a layer) of a wound dressing which isapplied to a wound.

The invention is particularly suited for application to topical andinternal wounds, for example traumatic injuries, surgical incisionwounds and open chronic wounds. Surgical wounds include those that arethe result of plastics or maxillofacial operations, mastectomy orcaesarean section.

The direction of the contractile force is influenced by the geometry ofcut in the material to form the lattice, the geometry of extension ofthe lattice and the geometry of the attachment points between thelattice or wound dressing and the tissue.

The open lattice or wound dressing can be applied to the wound siteusing any suitable technique and attachment means known in the art, forexample, adhesive, sutures, staples or topical pressure. Topicalpressure can be provided by compression bandaging or atmosphericpressure acting upon a cavity of reduced pressure relative to theexternal atmosphere. Attachment can be achieved at specific locations onthe open lattice or wound dressing or may cover the entire surfacethereof. For topical applications, attachment is preferably achieved byan area exceeding 50% of the total area of the open lattice or wounddressing in contact with the site of application. More preferably, fortopical applications, attachment is achieved by a pressure sensitiveadhesive, for example an acrylate-based adhesive. Typically, theadhesive forms a layer on the wound contact surface of the open latticeor wound dressing.

According to a further aspect of the invention there is provided amethod of manufacturing a wound dressing comprising the steps of,

-   -   (a) providing a first material,    -   (b) establishing the material in an extended conformation by        applying an extensive force to at least part of the material,        and    -   (c) retaining the material in the extended conformation by use        of a retaining means.

Preferably, the method of manufacture includes the step of forming atleast one slit and more preferably a plurality of slits in the materialto form a lattice. According to yet a further aspect of the inventionthere is provided a method of manufacturing a wound dressing comprisingthe steps of,

-   -   (a) providing a first material, and    -   (b) forming at least one slit in said first material to form a        lattice.

Preferably, the method of manufacture includes the steps of,

-   -   (a) applying an extensive force to at least part of the lattice        to establish the lattice in an extended or open conformation,        and    -   (b) retaining the lattice in the extended or open conformation        by use of a retaining means.

Examples of materials for use as the first material, include foams, suchas polyurethane foam and silicone-based elastomers.

An example of a suitable material for use as the retaining means is apolymeric film, such as polyurethane film. Other suitable materialsinclude polyester, polyethylene and polypropylene which can beperforated or extruded net.

In some embodiments, there is provided a wound dressing comprising abody of porous material, the body of porous material comprising aplurality of cuts which provide regions of flexibility within the body.

While the plurality of cuts provide regions of flexibility within thebody, they are not capable of rendering portions of the body frangible,such that the portions are relatively easily severable from the body.

Preferably the porous material is a wound packing foam suitable for usein negative pressure wound therapy (NPWT). Particularly suitable foamsfor NPWT include polyurethane foam, typically reticulated polyurethanefoam of very high free internal volume, e.g. 80% or higher, preferably90% or higher free internal volume. Typical foams used in NPWT haveporosities in the range 30-60 ppi (pores per inch) and mean porediameters in the range 300-800 μm. However, other suitable foams areknown in the art and may be equally employed. In general suitable foamshave an open porous structure, to allow transmission of the negativepressure to the wound bed, and sufficient mechanical strength to preventthe negative pressure (typically approximately 80-125 mm Hg belowambient atmospheric pressure) from collapsing the structure of the foam.

Suitably the cuts are slits. Herein this section and elsewhere in thisspecification, the term slit is intended to mean a cut which isgenerally long and thin, and preferably straight and linear. Inpractice, slits in foam are typically effectively 2-dimensional as theresilience of the foam means that the slit is essentially closed unlessthe material is stretched. Suitably the slits are from 10 mm to 70 mm inlength, preferably from 20 mm to 50 mm, especially from 25 mm to 40 mm.Slits of around 30 mm have been found to be particularly effective in atypical NPWT, though there is of course scope to vary this.

Providing cuts, e.g. slits, confers macroscopic flexibility, while notsubstantially affecting the microscopic mechanical properties of thebody, i.e. to resist compression under negative pressure. Thisflexibility allows the body of porous material to drape more easily,i.e. to conform to the shape of the wound to be dressed.

In a preferred embodiment, the body comprises at least one linear seriesof slits, each slit being separated from an adjacent slit by a gap. By“linear series of slits” it is intended to mean a plurality of generallylinear slits, each slit generally aligned along a straight line in aseries, with a gap separating each slit from adjacent slits in theseries. Generally it is preferred that the gaps are regularly sized.

Preferably the body comprises two or more parallel linear series ofslits, each linear series being spaced from the adjacent linear series.Preferably the spacing between the adjacent linear series is regular.

It will be clear to the person skilled in the art that the size of thegap between the slits, and the spacing between adjacent series, must besufficient such that the material retains structural integritysufficient for it to be handled, used in therapy and removed thereafterwithout breaking up. If the gaps and spacing were too small, the bodywould be too weak to achieve this. On the other hand, there is a desireto maximise the size and density of the slits to maximise drapeability.It is preferred that the minimum size of the gaps and/or spacing shouldcertainly be no less than the average pore diameter. It is morepreferred that gaps and/or spacing are at least 5 times the average porediameter; given that the average pore diameter for NPWT foam is in therange of 300-800 μm, this gives a gap or spacing of 1500 to 4000 μm,i.e. 1.5 to 4 mm. A gap of around 3 mm has been found to be particularlyeffective in a typical NPWT, though there is of course scope to varythis.

It is preferable that the spacing between adjacent linear series ofslits is kept reasonably small to provide the desired amount offlexibility and hence drapeability. Accordingly, it is preferred thatthe spacing is not more than 50 times the average pore diameter(typically from 15 mm to 40 mm depending on pore density), preferablynot more than 30 times than average pore diameter (typically from 9 mmto 24 mm depending on pore density). A spacing of around 3 mm has beenfound to be particularly effective in a typical NPWT, though there is ofcourse scope to vary this.

It is preferred that, where two or more parallel linear series of slitsare provided, adjacent series are linearly offset relative to eachother, i.e. it is preferred that the slits and gaps in adjacent seriesdo not line up, but are staggered. To put it another way, adjacentseries may be out of phase with each other. In one embodiment adjacentseries are offset such that the centre point of a slit in one series isaligned approximately with the gap in an adjacent series—similar to theway layers of bricks are offset in a wall. There is of course scope tovary the amount of offset.

This offset of adjacent series of slits allows for particularly gooddrapeability. When the body is curved the slits open up to form alattice type structure which is particularly suited to provide goodflexibility, and hence drapeability.

The slits may suitably pass completely through the thickness of thebody. Alternatively the slits may pass only partially though thethickness of the body, provided they pass through far enough to providethe desired flexibility to the body. In general it is preferred that theslits pass at least half way through the thickness of the body,preferably at least three quarters of the way through the body, andespecially substantially all the way through the body.

The present application is particularly suited to a wound dressingmaterial comprising a body of porous material which is relatively thin,although it could be used to impart flexibility to a body which isthick. In particular, the present invention is particularly suited to asheets of porous material which have a thickness of from 5 mm to 75 mm,preferably from 10 mm to 50 mm, especially from 15 to 40 mm, mostpreferably from 20 to 35 mm. In a very thin sheet (less than 5 mm)drapeability of the sheet is not such an issue, and where the thicknessis greater than about 75 mm, providing a plurality of cuts becomes lesseffective as a means of introducing flexibility. Thus the ranges set outabove represent sheets of thicknesses which are particularly well suitedto the present invention. The other dimensions of the sheet are notparticularly significant, although it may be observed that NPWT foam istypically sold in generally cuboid sheets with the dimensions of theedges of largest face being between 100 and 200 mm, e.g. a sheetmeasuring 100×200×30 mm is fairly typical.

It is generally preferred that the cuts are provided passing through theshortest dimension of the body. In particular it is preferred that thecuts (e.g. slits) are provided passing between the two largest faces ofa cuboid body (e.g. sheet), and especially that the cuts areperpendicular to the largest faces.

Where two or more parallel linear series of slits are provided, as setout above, this provides for good flexibility in a single direction ofcurve. When a body is curved around a surface, the inside of the body issubject to compression and the outside of the body is subjected totension (inside and outside being defined relative to the curve). Inwound dressings according to the present invention the cuts allow thebody to stretch when under tension, the cuts allowing deformation of theshape of the body (e.g. into a lattice), and this allows the body toeasily adapt to the desired curve. Where the cuts comprise slits in asingle orientation, the body will be well adapted to curving in adirection which causes tension perpendicular to the slits, but will beless well adapted to curving in another direction, i.e. where thetension produced is parallel to the slits. Therefore, the body is wellsuited to drape around a body with a single curvature (e.g. generallycylindrical), but not so well suited to draping around a more complexcurved object such as a generally spherical shape.

In a further embodiment of the present invention, the body comprises asecond set of slits passing at least partially through the body in adifferent orientation (preferably perpendicular) to the slits in the atleast one linear series of slits described above (the “first set ofslits”). It is preferred that the second set of slits also pass between,and are perpendicular to, the largest faces of the body. Additionalslits provided in this manner allow the body to curve more easily in asecond direction thus making it more suited to adapting to a complexcurved surface, i.e. curved in two planes.

In a preferred embodiment of the invention at least some of the slits inboth orientations intersect. Suitably the intersection of the slitseffectively provides a two-dimensional (2-D) slit. Preferably the 2-Dslit has an H shape, with a two parallel slits in one orientation beingintersected at their mid-points by a third slit in a perpendicularorientation. Such an H-shaped 2-D slit is well suited to the provisionof a relatively dense array of 2-D slits in the body. For example, rowsof H-shaped slits, each adjacent slit within the row alternating inorientation by 90 degrees, can be packed closely together, while obeyingthe minimum spacing requirements set out above.

In a preferred embodiment of the invention, the body comprises a firstset of parallel linear series of H-shaped slits in a first orientationand a second set of parallel linear series of H-shaped slits in a secondorientation. Preferably the second orientation is perpendicular to thefirst orientation. Preferably adjacent series within a set are offsetrelative to one another. Such an arrangement allows very close packingof the H-shaped slits, whilst maintaining a suitable spacing betweenneighbouring slits to retain the overall structural integrity of thebody. To allow close packing of the slits it is preferred that thelength of the two parallel slits (the “sides”) of the H-shaped slit areshorter than the perpendicular slit (the “cross-piece”) of the H-shapedslit. For example, the “cross-piece” may be from 10 mm to 70 mm inlength, preferably from 20 mm to 50 mm, especially from 25 mm to 40 mm,most preferably 30 mm and the “sides” are preferably around 6 mm shorterthan the “cross-piece”, especially around half the length of the“cross-piece”. Where the “sides” of the H are shorter than the“cross-piece”, it allows the “sides” of H-shaped slits in oneorientation to nest within the area bounded by “sides” and “cross-piece”of the H-shaped slit in the other orientation. This allows for veryclose packing of the H-shaped slits.

It should be noted that while a body having an array of H-shaped 2-Dslits is a preferred embodiment of the present invention, it is possibleto achieve a suitable 2-D array using other shapes, such as cruciformslits, or the like.

It should be noted that the cuts, e.g. slits, of the present inventioncan be provided by cutting a preformed body of foam, or the cuts couldbe provided during the process in which the body is manufactured (e.g.moulding). It is preferred that the cuts are provided by die cutting apreformed body.

In a further aspect, the present invention provides a method ofmanufacturing a wound dressing, the method comprising the steps of;

-   -   providing a body of a porous material; and    -   providing a plurality of cuts which provide regions of        flexibility within the body.

It is preferred that the cuts are provided by die cutting using an arrayof suitably sized and shaped blades to provide the desired cuts.

Details of preferred cuts, e.g. slits, are set out above, and it will beobvious to the person skilled in the art how to provide a suitable bladeto achieve the desired cut.

The cuts may be provided all the way through the body, or they may onlypass partially through the body.

The cuts may be formed in a batch, or they may be formed in a flowprocess.

In a further aspect the present invention provides a method of dressinga wound comprising administering a wound dressing as set out above tothe wound.

Preferably the method provides the step of applying a negative pressureto the wound through the wound dressing material, i.e. the method isNPWT. In general this can be achieved by providing a substantially fluidimpermeable sheet over the wound and wound dressing, thus defining asealed volume, and applying a negative pressure inside said sealedvolume. The seal need not be completely hermetic, but should besufficient to allow a suitable negative pressure to be sustained. Thesource of negative pressure, e.g. a pipe form a vacuum pump, can beprovided at a position such that it draws fluids from the wound bedthrough the wound dressing material.

Suitably the negative pressure is in the range of from 80 to 125 mm Hgbelow ambient atmospheric pressure.

In a further aspect the present invention provides the use of a wounddressing material as set out above in wound treatment, especially NPWT.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will be apparentfrom the following detailed description of the invention, taken inconjunction with the accompanying drawings of which:

FIG. 1 demonstrates the extension of a slit, in three stages, under anextensive force, indicated by the arrows F, and in a directionperpendicular to the longitudinal axis of the slit. The intermediate orsecond stage shows that the slit has been expanded to form a circle.

FIG. 2 is a plan view of a cutter for use in the manufacture of a firstembodiment of lattice according to the invention.

FIG. 3 is a plan view of the lattice formed using the cutter of FIG. 2,the lattice shown here in the open lattice or second conformation onapplication of a uni-directional extensive force applied perpendicularto the longitudinal axis of the slits.

FIG. 4 is a plan view of a further cutter having a different cuttingprofile to the cutter of FIG. 2 for use in the manufacture of a secondembodiment of lattice according to the invention.

FIG. 5 is a plan view of the lattice formed using the cutter of FIG. 4,the lattice shown here in the open lattice or second conformation onapplication of a bi-directional extensive force applied perpendicularand parallel to the longitudinal axis of the slits.

FIG. 6 is a schematic in plain view of yet a further a cutter, having analternative cutting profile to the cutter of FIGS. 2 and 4, for use inthe manufacture of a third embodiment of the lattice according to theinvention.

FIG. 7 is a plan view of the cutter manufactured according to theschematic of FIG. 6.

FIG. 8 is a plan view of the lattice formed using the cutter of FIG. 7,the lattice shown here in the open lattice or second conformation onapplication of a bi-directional extensive force applied perpendicularand parallel to the longitudinal axis of the slits.

FIG. 9 is a plane view of the lattice in the first conformation wherethe slits are substantially closed. The lattice is opaque and the slitsallow for no or substantially no visual inspection across the lattice.

FIG. 10 shows an array of blades adapted to form slits in a body of awound dressing material according to the present invention;

FIG. 11 shows a body according to the present invention curved in afirst direction;

FIG. 12 shows a body according to the present invention curved in asecond direction;

FIG. 13 shows a comparison of a body of foam according to the presentinvention with an un-cut body of foam;

FIG. 14 shows a second array of blades adapted to form cuts in a body ofa wound dressing material according to the present invention;

FIG. 15 shows a body according to the present invention cut with thearray of blades of FIG. 14; and

FIG. 16 shows the body of FIG. 15 curved in two dimensions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Like reference numbers refer to corresponding parts throughout thedrawings, description and examples.

Example 1

To create the wound dressing of example 1, a perforated sheet ofpolyurethane film was applied to the wound contact surface of a sheet of4 mm depth polyurethane foam (Allevyn, Smith & Nephew Medical Limited).

The wound contact surface is that surface which is placed adjacent to orin direct contact with the wound. The non-wound contact surface is thatsurface which is remote from or opposite the wound contact surface.

A cutter of specification shown in FIG. 2 (Cutter blade with 15 mmlength blades, linear spacing 5 mm, vertical spacing 5 mm) was used tocut slits in the sheet of polyurethane foam to form a lattice. Thecutting action also formed slits in the polyurethane film.

Following cutting, an extensive force was applied to the lattice in adirection perpendicular to the longitudinal axis of the cuts or slits toproduce an open lattice as shown in FIG. 3. A moisture permeabletop-film was heat laminated to the non-wound contact layer or surface ofthe open lattice. To the top-film, a polymeric film release sheet ofsufficient mechanical stiffness to resist the contractile force of theopen lattice was applied. After applying the release sheet the extensiveforce applied to the lattice was removed and the extended or openlattice was retained in the open lattice conformation by the releasesheet.

Example 2

To create the wound dressing of example 2, a perforated sheet ofadhesive polyurethane film was applied to the wound contact surface of asheet of 4 mm depth polyurethane foam (Allevyn, Smith & Nephew MedicalLimited). The adhesive surface of the film was covered by a siliconisedrelease paper. A cutter of specification shown in FIG. 2 (Cutter bladewith 15 mm length blades, linear spacing 5 mm, vertical spacing 5 mm)was used to cut slits in the sheet of polyurethane foam to form alattice. The cutting action also formed slits in the polyurethane filmand siliconised release paper.

The wound contact surface is that surface which is placed adjacent to orin direct contact with the wound. The non-wound contact surface is thatsurface which is remote from or opposite the wound contact surface.

Following cutting, the siliconised release paper was removed and anextensive force was applied to the lattice in a direction perpendicularto the longitudinal axis of the cuts or slits to produce the openlattice pattern as shown in FIG. 3. A new sheet of siliconised releasepaper was then attached to the wound contact surface of the perforatedadhesive film. A moisture permeable top-film was heat laminated to thenon-wound contact layer or surface of the open lattice. To the top-film,a polymeric film release sheet of sufficient mechanical stiffness toresist the contractile force of the open lattice was applied. Afterapplying the release sheet the extensive force applied to the latticewas removed and the extended or open lattice was retained in the openlattice conformation by the release sheet.

Example 3

To demonstrate the effectiveness of the wound dressing of example 2, thesiliconised release paper was removed from the perforated adhesive filmand placed, adhesive side down, upon intact skin. The polymeric filmrelease sheet was then removed. A uni-directional contractile force wasgenerated on the skin, upon removal of the polymeric film release sheet,and in a direction perpendicular to the axis of the cuts.

Example 4

To create the wound dressing of example 4, a perforated sheet ofpolyurethane film was applied to the wound contact surface of a sheet of4 mm depth polyurethane foam (Allevyn, Smith & Nephew Medical Limited).A cutter of specification shown in FIG. 4 (Cutter blade with 15 mmlength blades, linear spacing 5 mm, vertical spacing 2.5 mm) was used tocut slits in the sheet of polyurethane foam to form a lattice. Thecutting action also formed slits in the polyurethane film andsiliconised release paper.

The wound contact surface is that surface which is placed adjacent to orin direct contact with the wound. The non-wound contact surface is thatsurface which is remote from or opposite the wound contact surface.

Following cutting, the lattice was extended along two axes, x and y, asshown in FIG. 4. The extensive force was applied perpendicular andparallel to the longitudinal axis of the slits to produce an openlattice structure. A moisture permeable top-film was heat laminated tothe non-wound contact surface of the open lattice. To the top-film, apolymeric film release sheet of sufficient mechanical stiffness toresist the contractile force of the open lattice was applied. Afterapplying the release sheet the extensive force applied to the latticewas removed and the extended or open lattice was retained in the openlattice conformation by the release sheet.

Example 5

To create the wound dressing of example 5, a perforated sheet ofadhesive polyurethane film was applied to the wound contact surface of asheet of 4 mm depth polyurethane foam (Allevyn, Smith & Nephew MedicalLimited). The adhesive surface of the film was covered by a siliconisedrelease paper. A cutter of specification shown in FIG. 4 (Cutter bladewith 15 mm length blades, linear spacing 5 mm, vertical spacing 2.5 mm)was used to cut slits in the sheet of polyurethane foam to form alattice. The cutting action also formed slits in the polyurethane filmand siliconised release paper.

The wound contact surface is that surface which is placed adjacent to orin direct contact with the wound. The non-wound contact surface is thatsurface which is remote from or opposite the wound contact surface.

Following cutting, the siliconised release paper was removed and thelattice was extended along two axes, x and y, as shown in FIG. 4. Theextensive force was applied perpendicular and parallel to thelongitudinal axis of the slits to produce an open lattice structure. Anew sheet of siliconised release paper was then attached to the woundcontact surface of the perforated adhesive film. A moisture permeabletop-film was heat laminated to the non-wound contact layer or surface ofthe open lattice. To the top-film, a polymeric film release sheet ofsufficient mechanical stiffness to resist the contractile force of theopen lattice was applied. After applying the release sheet the extensiveforce applied to the lattice was removed and the extended or openlattice was retained in the open lattice conformation by the releasesheet.

The lattice of the wound dressing of example 5, having the polymericfilm release sheet removed, it shown in FIG. 5.

Example 6

To demonstrate the effectiveness of the wound dressing of example 5, thesiliconised release paper was removed from the perforated adhesive filmand placed, adhesive side down, upon intact skin. The polymeric filmrelease sheet was then removed. Upon removal of the polymeric filmrelease sheet, a contractile force was generated on the skin actingtowards the centre of the dressing.

Example 7

A similar process to that described for the wound dressing of example 5is employed to create the wound dressing of example 7. However, in thiscase, a cutter of specification shown in FIGS. 6 and 7 was used to cutthe slits. As can be seen from FIG. 6, the blades have three cuttingedges. A long cutting edge of 15 mm in length bridging two shortercutting edges of 7 mm in length. The two shorter cutting edges beingparallel to each other and perpendicular to the longer cutting edge.Each blade has a spacing with an adjacent blade which describes a squarearea having a side length of 3.75 mm. This spacing is demonstrated bythe shaded square portion in FIG. 6.

The lattice of the wound dressing of example 7, having the polymericfilm release sheet removed, it shown in FIG. 8.

An array of blades (10) mounted on a board is shown in FIG. 10. Eachblade (12) is a straight thin blade 30 mm long, and having a depth ofapproximately 30 mm. The blades are arranged in 20 parallel linearseries of blades (16,18), each series comprising a row of blades (12)arranged longitudinally, with a gap (14) of 3 mm between each blade (12)in the series. Each series is spaced from the adjacent series by a 3 mmspacing (15). Furthermore, adjacent series (16,18) are staggeredrelative to one another such that the gap between the blades on oneseries (16) aligns with the midpoint in the adjacent series (18).Accordingly, the blades within the array (10) are arranged like thebricks in a wall. Given this offset arrangement, it is convenient thatat the end of a series where a full 30 mm blade would extend beyond thedimension to be cut, blades of 15 mm length are provided; this allowsfor a neater array—once more, this is akin to half bricks at the end ofa row in a wall. Full length blades could be used at the ends, providedthey would not be problematic in the cutting process.

A body of NPWT foam (20) measuring 200×125×30 mm is cut using the array(10). It is cut by driving the array of blades (10) through the body(20) in a die cutting operation. This can be achieved using a press,typically a hydraulic press (not shown), also known as a clicker press.The blades are driven perpendicularly into and through the largest faceof the body (20), and perpendicular thereto, to form a plurality ofslits therein. The slits (21) formed are arranged in a plurality ofparallel linear series (26,28) of slits, each comprising slits (21) 30mm long separated by gaps (22), where material is left un-cut, which are3 mm long. Each series is separated by a spacing (24) 3 mm in width.When the body (20) is curved, as shown in FIG. 11, the slits (21) openup to form a lattice structure. Tension in the outer region of the body(20) as a result of the curving process is relieved through deformationof the body (20) which is facilitated by the slits (21) providedtherein. The arrangement of parallel offset linear series of linearslits is particularly suited to this as it form a regular latticestructure, as shown in FIG. 11.

In the embodiment shown in FIG. 11, an additional partial cut (30) hasbeen made running the length of the middle of the largest face of thebody (20), perpendicular to the slits. This allows the body (20) to beeasily split in two if this is desirable.

FIG. 12 shows another body (40) cut using the array of blades of FIG.10, this time without the additional cut (30). The body has been curvedin a different manner to that in FIG. 11. In this case the body has beenbent back on itself along its longest side, i.e. the 200×300 mm face hasbeen curved back on itself. The body (40) has opened via the slits (42)into an open lattice structure (44). This type of curving of the body(40) is not generally useful for a wound dressing application, but doesserve to demonstrate the flexibility and strength of the body (40).

FIG. 13 further demonstrates the ability of a body according to thepresent invention (40) to drape over a surface, in this case a leg, whencompared to an uncut body (46).

FIG. 14 shows an array (50) of blades adapted to form cuts in a body offoam in two orientations, the orientations being perpendicular to eachother. As with the array (10) in FIG. 10, the blades have a depth of 30mm. However, in the array (50) comprises H-shaped blades (52) comprisinga first blade element 30 mm long (54) (also termed “cross-piece”), withsecond (56) and third (58) blade elements (also termed “sides”) 15 mmlong located at the end of the first blade element (54), each end of thefirst blade element intersecting with the midpoint of the second andthird blade elements, thus defining a “wide H-shaped” blade. The arrayis made up of first set of eleven parallel linear series of H-shapedblades in a first orientation (called X for convenience) and a secondset of eleven parallel linear series of H-shaped blades in a second,perpendicular orientation (called Y for convenience). Adjacent serieswithin each set are offset in exactly the same manner as for linearblades. As can be seen from FIG. 14, the blades are spaced and arrangedsuch that a close packing of the blades as achieved, but each blade isalways approximately 5 mm or so from the nearest neighbouring blade. Itcan be seen that the “side” of a blade in the X-orientation nests withinthe region defined by the “cross-piece” and “sides” of a blade in theY-orientation. Such an array is suited to forming slits in a body toallow draping in two planes.

FIG. 15 shows a body (60) formed by cutting with the array of FIG. 14.The slits (62) are formed by pressing the array of blades (50) throughthe body (60) in the same manner as described above. H-shaped slits (62)are formed in the body (60) corresponding to the array of blades (50).As shown in FIG. 16, the body (60) is well adapted to curving in complexshapes.

It should be noted that the present description has focused on bodiesformed by a batch die cutting process. There are of course numerous waysof forming cuts in a body of porous material (e.g. laser cutting, highpressure liquid cutting), or the cuts could formed when the body itselfis formed (e.g. during a moulding process). Furthermore, these methodscould be applied in a flow process rather than a batch; this might bemore efficient for large production runs. All such variations are withinthe scope of the present invention.

Furthermore, it should be noted that, while the exemplified embodimentsform particularly preferred embodiments with excellent drapeability, itis quite possible that other arrangements of cuts will providesatisfactory results.

What is claimed is:
 1. A wound dressing apparatus, comprising: anabsorbent layer configured to transfer contractile forces to a woundsite to promote wound closure, the absorbent layer having a firstdimension and a second dimension, the second dimension perpendicular tothe first dimension, the absorbent layer comprising a plurality of slitsarranged in a pattern of separate parallel rows, wherein the pluralityof slits comprise first slits extending parallel to the first dimensionand second slits extending parallel to the second dimension, wherein theparallel rows comprise a first row extending along the second dimensionacross the absorbent layer and a second row adjacent to the first rowextending along the second dimension, the first row comprisingalternating first slits and second slits and the second row comprisingat least second slits, wherein the second slits of the second row arestaggered with respect to the second slits of the first row such thatevery first slit of the first row is directly adjacent to a second slitin both a first direction parallel to the first dimension and a seconddirection parallel to the second dimension; and a backing layerconfigured to be positioned over the absorbent layer.
 2. The wounddressing apparatus of claim 1, wherein the first dimension correspondsto a length of the absorbent layer.
 3. The wound dressing apparatus ofclaim 1, wherein the second dimension corresponds to a width of theabsorbent layer.
 4. The wound dressing apparatus of claim 1, wherein theabsorbent layer comprises a carboxymethylcellulose-based hydrofibre. 5.The wound dressing apparatus of claim 1, wherein the absorbent layer isopaque.
 6. The wound dressing apparatus of claim 1, wherein theabsorbent layer is configured to become transparent when wet.
 7. Thewound dressing apparatus of claim 1, wherein the slits are sized andconfigured as a result of being formed by a cutter.
 8. The wounddressing apparatus of claim 1, wherein the absorbent layer comprises afoam.
 9. The wound dressing apparatus of claim 1, wherein the slits areconfigured to be positioned in a plane parallel to a wound.
 10. Thewound dressing apparatus of claim 1, wherein each first slit and eachsecond slit pass entirely through a depth of the absorbent layer,wherein the depth is perpendicular to the first dimension and the seconddimension.
 11. The wound dressing apparatus of claim 1, wherein eachfirst slit of the plurality of first slits is directly adjacent a secondslit in both a first direction parallel to the first dimension and asecond direction parallel to the second dimension.
 12. The wounddressing apparatus of claim 1, wherein the second row comprisesalternating first slits and second slits.
 13. The wound dressingapparatus of claim 1, wherein each second slit is spaced apart from eachadjacent first slit.
 14. A wound dressing apparatus, comprising: anabsorbent layer configured to transfer contractile forces to a woundsite to promote wound closure, the absorbent layer comprising a patternof separate parallel rows comprising a first row comprising slitsoriented in a first direction and a second row comprising slits orientedin a second direction, the second direction perpendicular to the firstdirection; and a backing layer configured to be positioned over theabsorbent layer.
 15. The wound dressing apparatus of claim 14, whereinthe first row comprises slits oriented in the first directionalternating with slits oriented in the second direction.
 16. The wounddressing apparatus of claim 14, wherein the slits oriented in the firstdirection are staggered between adjacent first and second rows.
 17. Thewound dressing apparatus of claim 14, wherein the absorbent layercomprises a carboxymethylcellulose-based hydrofibre.
 18. The wounddressing apparatus of claim 14, wherein each slit oriented in the seconddirection is directly adjacent a slit oriented in the first direction.19. The wound dressing apparatus of claim 14, wherein each of the slitsoriented in the first direction and each of the slits oriented in thesecond direction pass entirely through a depth of the absorbent layer,wherein the depth is perpendicular to the first direction and the seconddirection.
 20. The wound dressing apparatus of claim 14, wherein eachslit oriented in the second direction is spaced apart from each slitoriented in a first direction.